A man died Sunday after a Muni bus pinned him under its tires at Fifth and Mission streets in San Francisco.

The pedestrian, who was not identified, was wearing a security guard uniform and appeared to be on his way to work when the crash occurred at 12:19 p.m. He crossed in front of the 14-L bus as it pulled out of the bus zone, a Muni spokesman said, and two sets of tires rolled over his legs. His lunch bag was found next to him. Police are investigating.

Christopher Wilkow was attending church at the Hub, a co-working space, when he noticed a commotion across the street. He ran out and discovered a man's legs sticking out from under the bus.

Wilkow said the driver didn't realize he had struck a pedestrian.

A woman called 911, and Wilkow and another person climbed under the bus. They found the man's right leg pinned.

"I just held his hand and kept telling him to breathe," Wilkow said.

Police and firefighters used wooden planks to lift the bus and free the victim, who was pronounced dead after being taken to a hospital.